In recent years, hard contact lenses use a material of higher oxygen permeability than conventional PMMA (polymethyl methacrylate) materials and these hard contact lenses have wide acceptance in the market as an oxygen-permeable hard contact lens. Because of their excellent oxygen permeability, these oxygen-permeable hard contact lenses permit oxygen supply from the atmosphere to the cornea, have a low risk of causing cacochymia of the cornea, and accordingly have relatively high safety. Further, unlike soft contact lenses made of a material containing a large amount of water, the oxygen-permeable hard contact lenses have good stabilities in dimension, shape, etc., are unlikely to be contaminated with bacteria, etc., allow easy handling, and accordingly can be said to be a lens of high safety. As the materials for the oxygen-permeable hard contact lenses, there have conventionally been proposed various materials, for example, cellulose derivatives [e.g. CAB (cellulose acetate butyrate)], copolymers of a silicone-containing (meth)acrylate and an alkyl (meth)acrylate, styrene derivatives, and copolymers of a fluorine-containing (meth)acrylate and an alkyl (meth)acrylate. In recent years, copolymers composed mainly of a silcione-containing (meth)acrylate or a fluorine-containing (meth)acrylate have been proposed and, because of their very high oxygen permeability, are gaining increasing acceptance in the market. However, a contact lens material with high oxygen permeability made by using an increased amount of such a silicone-containing or fluorine-containing (meth)acrylate as a component for increasing oxygen permeability becomes to have reduced mechanical properties and are insufficient particularly in processability and impact resistance. Meanwhile, a contact lens material with improved procesability, mechanical strength and impact resistance, made by appropriately selecting an alkyl (meth)acrylate becomes to have low oxygen permeability.
Thus, at present there has not yet been developed any contact lens material having high oxygen permeability and a good balance in various properties such as mechanical properties, processability, dimensional stability, wettability by water and optical properties. As the oxygen permeability of contact lens is enhanced, the brittleness of the lens increases and the lens tends to be broken even by a small impact. This is a serial problem in practical application of contact lens.